RING OPENING POLYMERIZATION

Ring opening polymerization produces a small number of synthetic commercial polymers. Probably the most important ring opening reaction is that of caprolactam for the production of nylon 6:

Although no small molecule gets eliminated, the reaction can be considered a condensation polymerization. Monomers suitable for polymerization by ring opening condensation normally possess two different functional groups within the ring. Examples of suitable monomers are lactams (such as caprolactam), which produce polyamides, and lactons, which produce polyesters.

Ring opening polymerization may also occur by an addition chain reaction. For example, a ring opening reaction polymerizes trioxane to a polyacetal in the presence of an acid catalyst. Formaldehyde also produces the same polymer:

Monomers used for ring opening polymerization (by addition) are cyclic compounds that open easily with the action of a catalyst during the reaction.

Small strained rings are suitable for this type of reaction. For example, the action of a strong acid or a strong base could polymerize ethylene oxide to a high molecular-weight polymer.

These water soluble polymers are commercially known as carbowax.

The ring opening of cycloolefins is also possible with certain coordination catalysts. This simplified example shows cyclopentene undergoing a first-step formation of the dimer cyclodecadiene, and then incorporating additional cyclopentene monomer units to produce the solid, rubbery polypentamer:

Another example is the metathesis of cyclooctene, which produces polyoctenylene, an elastomor known as trans-polyoctenamer:

Chemische Werke Huls produces the polymer for use in blends with some conventional rubbers. This metathetic reaction has become an important synthetic tool in the polymer field.  Catalyzed polymerization of cycloolefins has been reviewed by Tsonis.